1. Field of the Invention
The present invention relates to an image forming apparatus including a recover toner box in which recovered toner is accommodated.
2. Description of the Related Art
There is well known a technique of recovering the toner remaining on a surface of an image bearing member such as a photosensitive drum and an intermediate transfer belt after transfer in order to accommodate the recovered toner in a toner box. The toner box is exchangeably placed in the image forming apparatus. A toner detecting sensor is provided in the toner box in order to detect an amount of toner accumulated in the toner box. The toner detecting sensor detects that the toner box is filled up with the accumulated toner, whereby a user can recognize an exchange time of the toner box.
However, simply accommodating the toner in the toner box through an inflow port provided in the toner box accumulates the toner in a chevron shape with a peak of the inflow port. Even if the toner detecting sensor detects an uppermost portion of the toner accumulated in the chevron shape, the toner detecting sensor detects that the toner box is filled up with the toner although the toner box has an accommodation space.
Therefore, for example, in a technique disclosed in Japanese Patent Application Laid-Open No. 2006-98743 (FIG. 1, FIG. 2, FIG. 3), the toner detecting sensor detects the toner box is filled up with the toner after the uppermost portion of the toner accumulated in the toner box is flattened using two screws that convey the toner in opposite directions to each other.
However, in the toner box disclosed in Japanese Patent Application Laid-Open No. 2006-98743, the toner detecting sensor performs the detection on an end side of a container far away from the inflow port and in a detection space provided higher than a screw agitation region. In the configuration of the toner box disclosed in Japanese Patent Application Laid-Open No. 2006-98743, the toner entering the toner box through the inflow port is first accumulated on the inflow port side in a longitudinal direction of the container. The toner accumulated up to a level of one of the screws is gradually conveyed toward the side far away from the inflow port by one of the screws, and the toner is spread in the container. When the accumulation of the toner reaches the far side, the toner accumulated up to a level of the other screw which conveys in the opposite direction is conveyed toward the inflow port by the other screw. The accumulation of the toner is spread toward the inflow port side while an empty space in the container is filled with toner. In the configuration of the container, when the toner detecting sensor is provided on the end side of the container far away from the inflow port, the toner detecting sensor detects the toner before the toner is spread over the whole space by the other screw, and a determination that the container is filled up with the toner is made although the container can still accommodate the toner. When the toner detecting sensor is provided above the screw agitation region, the toner is accumulated higher than the screw, the toner excessively burdens the screw, and possibly the screw is locked.
Therefore, in order to prevent the screw lock, a full space detecting sensor is disposed while facing a side portion of the turndown screw. Further, the full space detecting sensor is disposed on a downstream side in a conveying direction of the turndown screw, which allows the full space to be detected after the accumulated toner is spread over the whole container.
However, the following problem is generated when the full space detecting sensor is disposed at the position in the container having the turndown screw. As disclosed in Japanese Patent Application Laid-Open No. 2006-98743, in the case of the turndown conveyance, the toner is accumulated from a front side of the container and, at the same time, the toner is returned by the turndown screw. At this point, the toner near an entrance is returned to a sensor detection portion. Therefore, before the toner is spread over the whole container, the toner is accumulated in the sensor facing portion, and sometimes the sensor detection portion falsely detects that the container is filled up with the toner.